Extraction of hydrocarbons



enema A r. 13, 1948 Benjamin G. Wilkes, Jr., Wiikinsburg, Pm, aslilnor to'Carbide and Carbon Chemicals Corporation, a corporation oi New York Serial No. 587,221

No Drawing. Application April I, 1945,

6 Claims. 01.. ice-14.35)

This invention relates to the separation oi mixtures of hydrocarbons into fractions having different chemical compositions. More especially it concerns the selective extraction oi hydrocarbon mixtures containing paraillns, cycloparaflins,

oleflns, diolefines and aromatic hydrocarbons, or

two or more oi these types thereof, employing a highly efllcient stable solvent which is liquid at the extraction temperature and which is highly selective for the more unsaturated hydrocarbons.

One of the more important objects of the invention is to provide a novel and eillcient method for separating a mixture oi parafllnlc and non-parafllnic hydrocarbons into portions one oi which is richer in the more parailinic components of the original mixture and the other oi which is richer in the less parafllnic components. Another object is to provide ior separating from hydrocarbon oils components having greater chemical unsaturation from components having less chemical unsaturation or from .parafilnic components in manner to produce refined oils of relatively paraflinic character. These and other objects will be evident as the description proceeds.

This invention is based upon the discovery that hydrocarbon compositions containing nonparaiflnichydrocarbons, such as those oi the naphthenie, olefinic, and aromatic series, with or without paraflinic-hydrocarbons, may be eifectively separated into fractions respectively richer and poorer in the chemically less saturated components by fractional extraction with certain selective solvents that are relatively high boiling. Hydrocarbons selectively dissolved by these solvents are readily separated from the resultant extract either by simple distillation or by steam distillation of the hydrocarbons irom the extract. The solvents possess high selectivity for the more saturated hydrocarbons.

In accordance with this invention, a hydrocarbon mixture containing parafllnic and non-paraflinic hydrocarbons, or one containing hydrocarbon components having varying degrees of chemical unsaturation, has admixed therewith a suitable quantity of an organic liquid containing at least one cyanoalkyl group directly connected with a sulfur atom, an omgen atom or an amino nitrogen atom.

A preierred group oi the selective solvents oi the invention may be designated by the iormula a A--XC2H4CN wherein A represents a methyl, ethyl,

or -cr ncHRoR' group; x designates s, 0,01

NR"; R and'R" respectively represent either hydrogen, or a methyl or ethyl group; and R represents either hydrogen or a methyl, ethyl. CH:CH2CN or CH:CHROCH2CH:CN group.

The monocyanoethyl derivatives of the aforesaid iormula but wherein A designates an alkyl group or a CHaCI-IROR group wherein R represents an alkyl radical are much less effective in the process than the other extractants herein disclosed when used in the anhydrous state due to a relatively high miscibility with mixtures of all? phatic and aromatic hydrocarbons. Admixture with water decreases the solvent power oi these compounds for saturated hydrocarbons while retaining an adequate solvent power ior aromatic and other unsaturated hydrocarbons. However, the highly selective solvents which do not require resort to the use of aqueous dilution oi the solvents are preferred.

High boiling compounds having outstandingly high selective extraction capacities for the more unsaturated components 01 hydrocarbon mixtures may be produced by reacting, in the presence of an alkaline condensation catalyst, olefinecyanides such as acrylonitrile with compounds having a suitably reactive hydrogen atom, such as hydrogen sulfide, ammonia, water, the lower monohydric alcohols, the monoand polyalkylene glycols such as ethylene glycol, propylene glycol, and the diand triethylene glycols: the monoalkyl ethers of such glycols, such as the methyl and ethyl ethers oi ethylene and diethylene glycols; and the primary and secondary amines, including the monoand polyalkylene amines such as ethylene diamine and diethylenetriamine. i

Among the compounds thus produced which have been found to possess remarkable selectivity in the removal oi the more highly aromatic con- I stituents oi hydrocarbon mixtures may bemen-' tioned ethylene glycol di(p-cyanoethyl)ether, NC-CzHr-O-C dim-cyanthe corresponding amine and ether,

NC-CaHa-N-C :HuCN

and NC-CzHwO-CN.

Examples of compounds useful as extractants include: ethyl p-cyanoethyl sulfide. fl-hydroxytivity for the aromatic and the more unsaturated components of hydrocarbon mixtures but they possess as a class this high selectivity over a fairly wide temperature range including temperatures around atmospheric. The treated hydrocarbon mixture readily separates into extract and rafilnate phases. Furthermore, the solvent is stable under the conditions of its use and does not react with components of the mixtures being extracted. The solvent and the hydrocarbons of the extract phase are separated readily either by simple distillation, steaming, or by other means, such as washing or leaching with water. The relatively high solvent power of these selective solvents for aromatic and the more unsaturated components makes unnecessary the use of large proportions of the solvents. Because of the high selectivity of these extractants at atmospheric temperatures, they may be employed ei-' fectively without recourse to refrigeration, or high temperature treatment and the like, which are sometimes used to improve the selective solvent action of extractants for certain hydrocarbons.

According to one form of the invention the hydrocarbon mixture is flowed in intimate countercurrent contact with a stream of the high boiling selective solvent. Some of the solvents employed in this invention are water-soluble or water-miscible while others are relatively waterinsoluble. Thus, hydrocarbons selectively dissolved by these solvents are in general preferably separated from the resultant extract by steam distillation of the hydrocarbons from the extract.

By applying the process to a hydrocarbon mixture of narrow boiling range, for example, one boiling within a range of 0., it is possible to recover substantially pure hydrocarbons such as toluene, benzene, hexane, cyclohexane. styrene,

commercially practicable manner. Hydrocarbon ethyl benzene, the xylenes and butadiene in a 4 mixtures derived from the distillation or cracking of petroleum, or coal tar hydrocarbons, and particularly mixtures containing hydrocarbons which have between-i and 10 carbon atoms in the molecule. may be effectively treated by the process.-

According to one preferred form of the invention a liquid hydrocarbon mixture to be separated into components of different degrees of chemical unsaturation. or of diflerent structural configurations, is flowed into intimate countercurrent contact with a stream of a high boiling solvent having at least one -CH2CH2CN group directly connected with an atom of S, or O, or an amino nitrogen. The extraction may be performed under atmospheric pressure, or at pressures above or below atmospheric, in an extraction'column or in a series of interconnected columns or batch extractors. Temperatures around 30 0. conveniently may be used. At this temperature the solvents such as di(,8-cyanoethyl) sulfide and the corresponding amine and ether are miscible in all proportions with benzene, and are almost entirely immiscible with paraflln hydrocarbons. A single stage extraction at 25 C. of a mixture containing 50% of benzene and 50% of cyclohexane by volume, with an equal volume of di(p-cyanoethyDamine yielded an aromatic or extract hydrocarbon fraction containing 85.4% of benzene and a rafllnate hydrocarbon fraction containing 38.2% 0! benzene. A continuous countercurrent or multiple stage extraction of a mixture of equal parts of benzene and cyclohexane also will yield at equilibrium extracted hydrocarbons containing approximately of benzene.

This value can be increased to a maximum of of benzene by reflux enrichment, which is accomplished by recovering from the extract layer the contained hydrocarbon rich in toluene; and returning'some of this to the extraction column with the mixture to be extracted. The ramnate of this system without enrichment contains approximately 73% of cyclohexane. By increasing the solvent-hydrocarbon ratio to 2:1, a raflinate completely denuded of benzene and containing less than 1% of di(p-cyanoethyl)- amine may be secured.

Table A indicates the comparative eflectiveness of two extractants, including one of the solvents of the present invention. The extraction index 01 comparison is based upon a single-stage extraction at 25 C. of a mixture of aromatic and aliphatic hydrocarbons havingthe compositions described in Table A.

The index= concentrations of the hydrocarbon content of the feed. raiilnate and extract layers.

Solvent A was di i sulfide; and solvent B (for comparison used Table A m h I l 2 3 4 benzene.. 307 benzene. 507 toluene..-.-.-- toluene. g v w n composition. p cent by volume 7 a mm" i i, B 0

ven Solvent-hydrocarbon rnfln 1:1... l:l.- 1:1.. 1:1. Composit :1 cl hydrocarbons from lolvent layer, per cent n 87 68 8i. Composition of hydrocarbons from raihnatc layer ar cent aromatic.- 22 19 43 44. Per cent of total aromatic hydrbcarbons recovered solvent layer--.. 4o r\1 Selectivity imle 8.5. 4.6- 5.7 l 1.6.

9a-llt 0., and containing a small percentage of aromatic hydrocarbons.

was diaminoethyl sulfide which is known to be an excellent aelemive to designate an aliphatic hydrocarbon mixture boiling over the range o! conventional The following examples are presented merely to illustrate certain forms of the invention. I

Example 1 A raw neutral Mid-Continental oil stock having a viscosity index of 60, measured byA. S. '1.

method D567, was extracted at 70 C. in a single stage by mixing .it with an equal volume of diq'e-cyanoethyl) amine. The rafllnate which separated upon standing contained less than 0.2% by weight of dicyanoethylamine which was readily removed bywashingwith water, yielding an oil with a viscosity index of 71.

The extract was diluted with water and then separated into an aqueous solvent layer and a firm sticky dark amber resin evidently devoid of parafl'inic oils. The solvent was recoverable from the aqueous solvent layer by distillation to remove the water.

Example 2 Into each of nine vessels was introduced an intimate mixture composed of three volumes of di(,e-cyanoethyl) sulfide and one volume of an equivolume mixture of toluene and Troluoil." Each of the mixtures. then was permitted to stratify, forming a lower extract layer and an upper raillnate layer. The ramnatelayers were successively conducted in stages toward the ninth vessel where three volumes of fresh solvent were introduced during each batch transfer. The extract layers were progressively conducted toward the first stag vessel where one volume of the hydrocarbon mixture was introduced with each batch transfer. After equilibrium had been reached, as established by the constancy of the composition of the final railinate and extract layers, an extract phase was secured, the hydrocarbon portion of whieh'contained 94.1% of toluene. Complete recovery of the toluene was 6 parafllnic hydrocarbons, as indicated in the following example.

Example 3 A four-stage batch extraction of a mixture of equal volumes of toluene and TroluoiP' with di(p-cyanoethy l)amine was conducted at 25. C., using a 3:1 solvent-hydrocarbon feed ratio by volume. Fresh solvent was added at the fourth stage, and the ramnate was recovered from that stage. The hydrocarbon mixture was introduced at the first stage, and the extract layer was re- The cyanoalkyl amine solvents of the invention are more efllcient extractants than are the corresponding cyanoalkyl sulfides for the production of aromatic-free rafilnates, and achieve these results at lower solvent-to-feed ratios. Theformer possess the further advantages over the cyanoalkyl sulfides of relatively mild odoryahd lower melting point.

Example 4 The data presented in Table B are the results of single-stage extractions of certain representative mixtures containing saturated hydrocarbons and/or hydrocarbons of different degrees. of chemical unsaturation. The extractions were conducted at 25 0., using equal volumes of the hydrocarbons and of the solvent. In the analysis of the extract fractions, the hydrocarbons were removed by steam distillation and recovered.

Table B H ExtraetedHydrocu-bon Rafllnate J Original Hydrocarbon Solvent Composition(por cent :32

by volume) by Composition (per cent by Composition (per VOL by volume) VOL cent by volume) ume ume 95 toluene 40 o toluene. 35o 'iroluoil" 25 groluoil." s yrene s ene. 35% xylene 52 759i xylene. 85.47 benzene. 74 38.27 benzene.

ctyclohaxane 7 cyclohexane. s eno 5 ene..

7 et yl benzene l 48 fifiqgtet yl benzene. s rene s ne. 74.6 6 et yl benzene. 64 {83% etlz y l benzene.

In Table B, liliisilveni: C is diwcyanoethybether; solvent D is di(fl-cyanoethyl)amine; and solvent E is di(fi cyanoethyDsu e achieved in the extract phase, the rafilnatelayer being substantially free from aromatic hydrocarbons. The raflinate contained only about 1% by volume of dicyanoethyl sulfide. The hydrocarbons were recovered from the extract by steam distillation at 125 C.

A substantially complete separation of the The single stage extraction of benzene from cyclohexane demonstrates the outstanding selectivity of dicyanoethylamine as a. solvent for arohydrocarbon mixture into a pure toluene extract phase and an aromatic-free rafilnate may be secured by a continuous counter-current extraction procedure wherein the outgoing extract phase is contacted with a toluene-enriched feed in a "reflux enrichment operation. Di(p-cyanoethyl) amine has a greater solubility for aromatic hydrocarbons such as toluene than has di(p-cyanoethyl) sulfide. These solvents have matic hydrocarbons. A continuous countercurrent extraction or a multiple stage batch extraction of a. mixture of equal parts of benzene and cyclohexane yields at equilibrium an extracted hydrocarbon mixture containing about of benzene. By increasing the solvent to hydrocarbon feed ratio to 2:1, a rafllnate may be obtained that is completely denuded of benzene and contains less than 1% of dicyanoethylamine. somewhat lower degree of selectivity is apparent in the extraction of styrene from xylene with dicyanoethyl ether. However, even in the difilcultly extractable styrene-ethylbenzene system, a very very low and substantially equal solubilities for 76- substantial selectivity is evidenced.

. Example 5 Thetollowing data are based upon batch extractions oi equivolume mixtures oi toluene and Troluoir' with a like volume of the extractant In each instance the concentration or solvent in the railinate layer was less than 1% by volume.

Table ition extracted was 50% by volume toluene 'lh h drocarbonoom I e y h cebeing"Troluoll' Solvent r o n 1 K lzl Solvent-h drocarbon ratio Composlt on oi hydrocarbons in extract layer, per cent aromatics" corkngsition o hydrocarbons in atelayer, cent aromatics.

Per cent of tot aromatic hydromrbons in the extract layer Solvent F-was p-edvianoethyl-fi-hydroxyethyi other; solvent G was ethylene lyco ol-cyanoethybether; solvent H was diethylene glycol di& c anoetlgnetber; solvent I was fi-cyanoethylfihydroxyet yl en] do; an

ethylamine.

The. data presented in Table C illustrate the highly selective nature of the cyanoethyl ethers of the glycols in the extraction of aromatic hydrocarbons i'rom non-aromatic hydrocarbons. It will be notedthat solvent G is also remarkably eflicient as an extractant, removing 42.5% of the total toluene of the system in a single batch process at a solvent-hydrocarbon ratio of only 1:1.

Solvents F and G may be made by reacting acrylonitrile and ethylene. glycol containing a small amount .of aqueous potassium hydroxide. The reaction mixture is neutralized with hydrochloric acid, the solid salts separated, and the liquid iractionally distilled under vacuum. Solvent F boils at 115-117 C. under 2 mm. of mercury, absolute pressure; and Solvent G boils at 165 C. under mm. of mercury, absolute pressure.

Solvent H can be made in similar manner by substituting diethylene glycol for the ethylene glycol. Solvent I-I boils at 205-210 C. under an absolute pressure or 3 mm. of mercury.

Solvent I may be made by reacting at 50 C. acrylonitrile and mercantoethanol containing N- methyl morpholine as catalyst, and distilling the reaction mixture at a pressure or 5 mm. 0! mercury. Solvent I boils at 160-165 C. at that pressure.

Solvent K may be made by .reacting acrylonitrile and monoethanolamine at 20-25 0., and

fractionating the residual mixture under a high vacuum.

- I-;.' I he;;process oi the invention is applicable for aflln hydrocarbons may have the oleflnes absorbed by extracting such a mixture with the selective solvents of the invention.

It will be seen that this invention eflects the separation, from mixtures of hydrocarbons, and preferably from those mixtures having boiling ranges not greater than about 50 C. of hydrocarbons having diilerent degrees of chemical unsatu- 8 I ration or or diiierent structural configurations. The separation may be eilected at room temp r ture, or at temperatures either below or above room temperature. Preferably the hydrocarbons are recovered from the extract phase thus separated by the usual steam distillation or the equivalent.

I claim:

1. Process for separating a hydrocarbon mix ture into portions respectively enriched in the chemically-more unsaturated constituents and in the chemically less unsaturated orsaturated constituents of such mixture, which comprisesextracting the hydrocarbon mixture with .a N-di- (p-cyanoethyl) amine. v

2. Process for separating a, hydrocarbon mixture into portions respectively enriched in the chemically more unsaturated constituents and in the chemically less unsaturated or saturated constituents or such mixture, which comprises extracting the hydrocarbon mixture with an aliphatic dicyano amine formed by reacting acrylonitrile with an alkylene amine.

3. Process for separating a hydrocarbon mixture into portions respectively enriched in the chemically more unsaturated constituents and in the chemically less unsaturated or saturated constituents oi such mixture, which comprises extracting the hydrocarbon mixture with a dicyano imino compound formed by reactingac'rylonitrile with a polyalkylene amine.

4. Process for separating a hydrocarbon mixture into portions respectively enriched in. thechemically more unsaturated constituents and in the chemically less unsaturated or saturated constituents of such mixture, which comprises extracting the hydrocarbon mixture with a di- (cyanoethyDamine.

5. Process for separating a hydrocarbon mixture into portions respectively enriched in the chemically more unsaturated constituents and in the chemically less unsaturated or saturated constituents of such mixture, which comprises extracting the hydrocarbon mixture with an allphatic cyano compound formed by reacting acrylonitrile with a compound selected from the class consisting of the monoand polyethylene amines, and the monomethyl and monoethyl ethers of ethylene glycol, of diethylene glycol and of triethylene glycol.

6. Process for separating a hydrocarbon mixture into portions respectively enriched in the chemically more unsaturated constituents and in the chemically less unsaturated or saturated constituents of such mixture, which comprises extracting the hydrocarbon mixture with p.p'-di- (cyanoethylamino) ethane.

' BENJAMIN G. WILKES, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,813,946 Nicodemus July 14, 1931 1,919,752 Schmidt et al. July 25, 1933 2,023,375 Van Dijck I Dec. 3, 1935 I 2,092,739 Van Diick II Sept. 7, 1937 2,139,000 Cohen Dec. 6, 1938 2,160,607 Van Dijck III May 30, 1939 2,162,963 McKittrick June 20,1939 2,205,996 Van Wijlr June 25, 1940 2,285,696 Dunn I June 9, 1942 2,288,126 Dunn et al. III June 30, 1942 2,290,636 Deanesly July 21 1942 

